The present invention relates to a process for covering a flat-lying blank, preferably made of cardboard, with a cover, which are in particular applicable in the production of book covers, in which the covering takes place in cycles in a number of working stations, and in which each working station carries out a number of procedural steps within a predetermined overall cycle time.
The present invention relates further to an arrangement for covering a flat-lying blank, preferably of cardboard, with a cover, in particular, for the production of a book cover, comprising at least one working station, whereby a predetermined overall cycle time is assigned to each working station, and whereby each working station comprises at least one working means, to which at least one sub-cycle time is assigned.
A process and an arrangement of this type are prior art arising out of the manufacture and sale of book cover machines of the type “BDM Speed” by Hoerauf. A book cover machine of this kind operates with a changeable number of cycles per minute, whereby the blank is transported in cycles through a number of working stations of the machine and provided with the cover. The manufacturing process includes hereby at least the cycles “joining”, “front and rear folding”, “lateral folding” and “pressing”. If for example, the machine operates at 60 cycles a minute, the overall cycle time of one cycle amounts to exactly one second. Within this overall cycle time, a number of procedural steps have to be carried out, whereby in addition to the actual work steps in the stations, the transport into the station must also be carried out within this overall cycle time. During the first cycle “joining”, for example, the cover and the blank are transported into the first station, the cover is coated with glue and brought together with the blank. In a subsequent cycle the blank with the cover is transported into a folding station, the edge of the cover is prepared and finally folded and pressed onto the blank. Each of these procedural steps within the overall cycle time of a cycle is assigned a sub-cycle time. The drive and control concept of the machine enables the procedural steps of one cycle to be carried out always in the same ratio to the overall cycle time, in spite of the variable cycle rate of the machine. This means for the folding station that in designing the machine, when once a sub-cycle time “folding and pressing” is assigned to the folding means amounting to a quarter of the overall cycle time, then this ratio of the sub-cycle time to the overall cycle times could no longer be changed. In the case of an increase in the cycle rate of the machine, that is, an increase in the production speed, the overall cycle time for each individual cycle is reduced. In accordance with the once pre-determined ratio of the respective sub-cycle time to the overall cycle time, the sub-cycle time for each procedural step in a station is also reduced.
The known machine has hereby the disadvantage that the duration of the procedural steps which determine the quality of the finished book cover, and the sub-cycle time of the corresponding work means are only changeable by means of a change in the overall cycle time, that is, in the cycle rate and the production speed. Materials which are difficult to process, for example particular glue types or cover materials having a high degree of stiffness can only be processed at low cycle rates and reduced production speed, as these materials require relatively long sub-cycle times for application of the glue and for the procedural step “folding and pressing” in order to be processed properly.
It is an object of the present invention to improve a process of the above named type with regard to its adaptability to various properties of the material to be processed, and to increase the flexibility of an arrangement of the above mentioned type.
This object has been achieved in accordance with the present invention in that in the process, at least a sub-cycle time of a procedural step is adapted to the material to be processed while the overall cycle time remains constant. In the case of the arrangement, the object has been achieved in that the ratio of the sub-cycle time assigned to the working means is variable in relation to the overall cycle time.
An embodiment of this type has the advantage in that in each working station the duration of the quality-determining procedural steps can be adapted to the requirements of the material to be processed, without changing the production speed. In the joining station, for example, it is possible to reduce the speed of the cover when the glue is being applied, when a highly viscous glue or a glue which may spray drops of glue during application, is processed. As at the beginning of each cycle the blank is transferred from the foregoing working station, each station has for its procedural steps only the duration of the predetermined overall cycle time at its disposal. This ensures a fault-free interaction of all the successive working stations with one another. Within the overall cycle time of a cycle it is however advantageous to design the speeds of the individual work means to be variable, so that in particular the quality-determining procedural steps are assigned an optimal portion of the cycle time. This is then particularly simple when in each working station a drive for the respective working means is provided and this drive comprises at least one motor driveable at a non-uniform angular velocity. Motors connected to a control system for varying the ratio of the sub-cycle time assigned to the working means in relation to the overall cycle time are particularly advantageous.
In particular when an edge of a cover applied to a blank is folded over, an embodiment of this kind has the advantage in that the duration of the quality-determining procedural step “folding and pressing” can be set without altering the speed of production. At a constant remaining cycle rate of the machine, the sub-cycle “folding and pressing” can be chosen in such a way that the cover to be processed is optimally folded over.
Particularly advantageous is when at a constant remaining overall cycle time the duration of the procedural step “folding and pressing” is extended and the duration of the procedural step “preparing” is shortened. This permits the reliable processing, with relatively high cycle rates and production speeds, of difficult cover materials, for example material with a high degree of stiffness. As a result of the extended pressing-on time, the glue has more time to adhere, thus preventing the folded edge from separating from the blank again, even in the case of thicker or stiffer covers. In the case of this arrangement, while maintaining a constant overall cycle time, the sub-cycle time “folding and pressing” assigned to the folding means is extendable while the sub-cycle time “preparing” assigned to the folding means can be reduced.
Even more scope for adjustment and an even higher variability for the procedural step “folding and pressing” can be achieved in that, at a constant remaining overall cycle time, the duration of the procedural step “folding and pressing” is extended and the duration of the procedural step “transport”, in which the blank provided with the cover is transported into the folding station, is shortened. In this arrangement this is achieved in that, at a constant remaining overall cycle time, the sub-cycle time “folding and pressing” assigned to the folding means is extendable and the sub-cycle time “transport” assigned to the transport means can be reduced.
In a further advantageous embodiment of the arrangement according to the present invention it is provided that the drives are connected with a control system for varying the ratios of the sub-cycle time “folding and pressing” to the overall cycle time. A variation of the above mentioned ratio can be very simply carried out by the operating personnel, for example, on a computer monitor.
In order to achieve a high variability and an easy adjustment it can be provided that all folding and transporting means are driven by their own drive motor which is connected to the control system. This embodiment has, however, the disadvantage in that a very large number of single motors would have to be provided when a number of folding means are provided.
For this reason, cam plates for driving the folding means are applied in the book cover machine described above as prior art. The cam plates for the various folding means of a folding station are located in the form of a cam plate packet on a joint drive shaft and are driven by a motor having uniform angular velocity. The angular velocity of the cam plates is chosen according to the cycle rate of the machine in such a way that each cam plate rotates once around its axis during the length of one overall cycle time. Because of the cam plates, driven at a uniform velocity, the known machine has the disadvantage described above, that the ratio of the sub-cycle time assigned to the folding means to the overal cycle time is constant and cannot be changed. The ratios of the sub-cycle times to the overall cycle time is set by the geometry of the cam plates and cannot be changed once the machine is in operation.
It is therefore advantageous that the drive of the folding means comprises at least one cam plate driveable at a non-uniform angular velocity. This permits the sub-cycle time “preparing” assigned to the folding means to be shortened, in that the angular velocity of the cam plate in this area is increased and the sub-cycle time “folding and pressing” assigned to the folding means to be extended, in that the cam plate in this area is driven with reduced angular velocity. Overall, however, it is provided that the cam plate rotates once around its axis during one overall cycle time. The amount of required overall time for the folding process does not change because of this, so that the interaction of the working stations upstream and downstream continues to be ensured.
In a further embodiment of the present invention it can be provided that the folding means for “folding and pressing” consists of a brush. The folding of the edge can be carried out in a process of particularly high quality and without creasing. In addition it can be advantageous when the folding means for “folding and pressing” is separated from the folding means for “preparing”. In order to prevent the cover coming off the blank when the edge is being folded, it can be advantageous to assign at least one clamping device for the blank provided with the cover to the folding means for “preparing”.